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[摘要]：A new unexpected reaction of 1-(4-fluorophenyl)-2-(4-pyridyl)ethanone with 3-aminopyrazole, involving loss of a 4-pyridylmethyl group, afforded 4,6-bis(4-fluorophenyl)-5-(4-pyridyl)-1H-pyrazolo[3,4-b]pyridine in good yields. Investigation of the features of this cyclization led to the development of a new 3-component coupling for the synthesis of pyrazolo[3,4-b]pyridines, from a ketone, an aldehyde, and a 3-aminopyrazole using acid catalysis and a protic solvent. The study of the scope of this reaction showed its remarkable versatility and its usefulness in the prepn. of other bicyclic systems, such as thieno[3,2-b]pyridines, pyrrolo[3,2-b]pyridines, imidazo[4,5-b]pyridines, furo[2,3-b]pyridines, isoxazolo[5,4-b]pyridines, and isothiazolo[5,4-b]pyridines. The 3-component nature of this reaction makes it suitable for the prepn. of combinatorial libraries. |
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